Added support for different core versions

While porting the energia msp430 core to MPIDE (just for a laugh, as you do) I found some parts of the multi-platform code slightly lacking.

This patch adds some extra platform variables to set the master include file for a core (WProgram.h / Arduino.h), and also the "Arduino" version of the core (the number set with -DARDUINO=xxx)

eg:

    platformname.core.version=23
    platformname.core.include=WProgram.h

Also better handling of string replacements in the bootloaders.txt file (to properly handle quote-encapsulated strings) as been implemented.